bundle2: no longer use 'retractboundary' in updatephases The new 'phase-heads' forced all added node to secret before advancing the boundary to work around the fact changesets were added as draft by default. This is no longer necessary since the changegroup part can now use the 'targetphase' parameter. Not doing this retract boundary call has a couple of advantages: * This makes implementing phases change tracking in the transaction much simpler since retract boundary can become a rare case. * Bundling secret changesets is not the norm. Exchange never does that and even for strip, the use-case is not common.Skipping the retract boundary will avoid useless work here. * Sending phase update on push can be simplified since we can rely on the behavior of 'cg.apply' for most of it. This means less phases update send for example. * We no longer needs to track and use the addednodes during unbundling. This make it possible to have multiple 'changegroup' and 'phase-heads' parts in the same bundle without them interfering with each others. The new part has not been part of any release yet so we do not offer backward compatibility yet. It is important to update this semantic before the 4.3 freeze happens.

bundle2: automatically add 'targetphase' parameter in writenewbundle If we are bundling secret changeset and the bundle will contain phase, we request the changegroup to be applied as secret. It will be useful for next patch as we are now sure that secrets changesets are applied as secret and not applied as draft then forced to secret.